1. Field of the Invention
The present invention generally relates to a torque point learning method and control method of a clutch, and particularly to a torque point learning method and control method of a wet friction clutch provided to the power transmission of vehicles.
This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in Japanese Patent Application No. 2001-085303 filed Mar. 23, 2001 and Japanese Patent Application No. 2001-085304 filed Mar. 23, 2001 and Japanese Patent Application No. 2001-093252 filed Mar. 28, 2001.
2. Description of the Related Art
In a power transmission device of vehicles, there are those which serially provide a fluid coupling (including a torque converter) and a wet friction clutch in the middle of a power transmission path from the engine to the transmission, and automatically disconnect/connect the wet friction clutch during a gear shift. Here, if a gear-in operation is made when the vehicle is not in motion, the clutch is thereafter automatically connected, and a creep is generated thereby. This point is similar to an ordinary AT vehicle.
Connection of the clutch will generate a clutch connection shock (so-called garage shock, etc.) when too fast, and much time will be required from the gear-in operation to the creep generation when too slow, and the driver will not know when to step on the acceleration (large time lag). Thus, in order to seek the successful combination of such clutch connection shock and shortened connection time, a control is performed so as to rapidly connect the clutch in the allowance region up to when the clutch begins to connect, and to slowly connect the clutch by switching the connection speed once the clutch begins to connect.
More specifically, the working fluid pressure for driving the disconnection/connection of the clutch is altered in accordance with the duty pulse output from the electronic control unit (ECU), and, when connecting the clutch from a disconnected state, a prescribed start duty is foremost output from the electronic control unit such that the clutch will be broadly connected up to a position near where the clutch begins to connect (this is referred to as a single connection), and a gradual connection duty is thereafter output from the electronic control unit in prescribed time intervals for gradually connecting the clutch.
The aforementioned control is an open control, and the ECU outputs a duty pulse pursuant to a predetermined prescribed program.
As shown with the broken lines in FIG. 11, the clutch connection control of the prior inventions foremost outputs from the ECU a prescribed start duty Dst"" so as to broadly connect the clutch up to a position near where the clutch begins to connect (this is referred to as a single connection control), thereafter outputs from the ECU in prescribed time intervals a prescribed gradual connection duty Dk"" so as to gradually connect the clutch, and, when reaching a prescribed gradual connection end duty Ded"", outputs a complete connection duty Dc"" (=0%) such that the clutch is completely connected.
The position where the clutch begins to connect; that is, the torque transmission starting point capable of initially transmitting a prescribed torque, is referred to as a torque point, and this torque point is used, for example, as a connection speed switching point by making the control unit learn such point, and a torque point plays an important role in the clutch control. The torque point is made a learning value because clutches have variations or individual differences caused by manufacturing errors or the like, and the torque point differs for each clutch.
Meanwhile, with respect to torque point learning, conventionally, in a dry friction clutch, a clutch stroke value for transmitting a prescribed torque was initially detected, and such value was learned as the torque point.
Nevertheless, in the case of a dry friction clutch, since the clutch plate is constantly sliding in the oil and the torque transmission is achieved with the clutch piston pressing the plates together, the concept of stroke does not exit in the first place. Moreover, although the clutch piston will make a stroke, the stroke length is small (approximately 2 mm for example). Therefore, it is not possible to adopt the method of detecting the clutch piston stroke and making this the learning value as with a dry [friction clutch.
Further, with a wet friction clutch, also considered may be a method of detecting the hydraulic pressure applied to the clutch piston. Nonetheless, a hydraulic sensor is expensive, and the detection of hydraulic pressure is difficult from a structural perspective. In addition, not only is there a problem with respect to the reliability of the detected value itself due to the large hydraulic pulse, there is also the problem in that individual variations exist since the same torque is not necessarily transmitted to the same hydraulic pressure value. Thus, this method may not be adopted either.
On the other hand, with respect to the clutch control and torque point learning, the following problems arise if the gradual connection duty output is commenced immediately after the start duty output. In other words, although the fluid pressure of the clutch piston chamber will rapidly rise pursuant to the output of the start duty, the clutch piston commences the pressing of the clutch plates after a small stroke (approximately 2 mm) of the initial allowance is made. The response will therefore be delayed for the stroke portion, and, when commencing the output of the gradual connection duty immediately after the output of the start duty, the response delay of such deviance will be carried over into the gradual connection. Since similar control is performed during the torque point learning, there is a problem in that the value of the connection side is learned rather than the true torque point of the clutch upon such learning. Moreover, there is an additional problem of the clutch connection shock becoming large upon employing the learning value deviating toward the connection side and due to the aforementioned response delay during the clutch connection control.
Meanwhile, as shown in FIG. 11, with respect to the clutch control, in reality, the torque point may vary due to disturbances such as individual differences, operational conditions, change in properties with time or the like of the clutch, and the optimum start duty value may vary or deviate as illustrated with Dst1xe2x80x2 and Dst2xe2x80x2. Moreover, it is not possible to detect such variance or deviation prior to renewing the torque point learning. Therefore, in this case also, if control is performed with the start duty value remaining at Dstxe2x80x2, the connection time lag will become large when deviating to Dst1xe2x80x2, and the connection shock will become large when deviating to Dst2xe2x80x2.
The following explanation is made with particular reference to the state upon starting the vehicle. FIG. 13 represents the state of the creep change when the gear-in operated is made (when the so-called garage shift is made) immediately before the vehicle is put into motion, and also illustrates changes in the revolution of the input side (pump) and output side (turbine) of the fluid coupling. Revolution of the input side of the fluid coupling may be replaced with engine revolution Ne (solid line), and the revolution of the input side of the fluid coupling, or the turbine revolution Nt (chain line), may be replaced with the clutch input side revolution as is.
At time t0, let it be assumed that the gear-in operation has been completed and that the clutch connection control has been commenced. Since the output side of the clutch is being stopped with a brake from the drive wheel side, the fluid coupling slides more in accordance with the connection of the clutch, and while the pump, which is the input side of the fluid coupling, revolves at a prescribed idle revolution equivalent to the engine revolution Ne, the turbine revolution Nt gradually decreases. The creep gradually increases thereby.
If the decrease of the turbine revolution Nt at the time of an appropriate start duty is line diagram J, when the appropriate value deviates to Dst1xe2x80x2 as shown in FIG. 11, the turbine revolution Nt becomes as illustrated with line diagram J1, and the time lag becomes large as a result thereof. Contrarily, when the appropriate value deviates to Dst2xe2x80x2 as shown in FIG. 11, the turbine revolution Nt becomes as illustrated in line diagram J2, and the connection shock becomes large as a result thereof.
The present invention was devised in view of the foregoing problems. An object of the present invention is to enable torque point learning in a wet friction clutch.
Another object of the present invention is to absorb the response delay during clutch connection, enable the accurate learning of a true torque point at the time of learning the torque point, and prevent a large clutch connection shock upon a standard clutch connection control.
A further object of the present invention is to yield redundancy and successfully combine the time lag and shock at the time of clutch connection even in cases where the optimum start duty value varies or deviates pursuant to disturbances.
The torque point learning method of a clutch according to the present invention is a method of learning a torque point of a clutch in a power transmission device of a vehicle in which a wet friction clutch is provided in the middle of a power transmission path extending from the engine up to the transmission, so that the disconnection/connection state of the wet friction clutch is controlled in accordance with the duty ratio of the duty pulse output from an electronic control unit,
wherein, when the aforementioned electronic control unit is caused to learn a torque point at which a prescribed torque is transmitted initially while the wet friction clutch is being connected from the disconnected state thereof, the value of the duty ratio of the duty pulse output from the electronic control unit is learned as the torque point.
Moreover, the torque point learning method of a clutch according to the present invention is a method of learning a torque point of a clutch in a power transmission device of a vehicle in which a fluid coupling at the upstream side and a wet friction clutch at the downstream side are provided in series in the middle of a power transmission path extending from the engine up to the transmission; a hydraulic supplying device is provided for supplying a working fluid pressure to the wet friction clutch; and the hydraulic pressure supplied from the aforementioned hydraulic supplying device is changed in accordance with the duty ratio of the duty pulse output from an electronic control unit, for thereby controlling the disconnection/connection state of the wet friction clutch,
wherein, when the aforementioned electronic control unit is caused to learn a torque point at which a prescribed torque is transmitted initially while the wet friction clutch is being connected from the disconnected state thereof, the aforementioned duty ratio is changed, while detecting the revolution of the input side of the wet friction clutch and the revolution of the engine, for gradually connecting the wet friction clutch from the disconnected state thereof, and, when the revolution of the input side of the wet friction clutch becomes less than the aforementioned engine revolution by a prescribed value of revolution during the foregoing process, the value of the aforementioned duty ratio at this time is learned as the torque point.
Further, the torque point learning method of a clutch according to the present invention is a method of learning a torque point of a clutch in a power transmission device of a vehicle in which a fluid coupling at the upstream side and a wet friction clutch at the downstream side are provided in series in the middle of a power transmission path extending from the engine up to the transmission; a hydraulic supplying device is provided for supplying a working fluid pressure to the wet friction clutch; and the hydraulic pressure supplied from the aforementioned hydraulic supplying device is changed in accordance with the duty ratio of the duty pulse output from an electronic control unit, for thereby controlling the disconnection/connection state of the wet friction clutch,
wherein, when the electronic control unit is caused to learn a torque point at which a prescribed torque is transmitted initially while the wet friction clutch is being connected from the disconnected state thereof, the aforementioned duty ratio is changed, while detecting the revolution of the engine, for gradually connecting the wet friction clutch from the disconnected state thereof, and, when the revolution of the engine has dropped by a prescribed revolution during the foregoing process, the value of the aforementioned duty ratio at this time is learned as the torque point.
Moreover, the torque point learning method of a clutch according to the present invention is a method in a power transmission device of a vehicle which serially provides a fluid coupling at the upstream side and a wet friction clutch at the downstream side, respectively, in the middle of the power transmission path from the engine up to the transmission; provides a hydraulic supplying device for supplying a working fluid pressure to the wet friction clutch; alters the hydraulic pressure supplied from the hydraulic supplying device in accordance with the duty ratio of the duty pulse output from an electronic control unit; and controls the disconnection/connection state of the wet friction clutch thereby, comprising the steps of:
respectively detecting the revolution of the input side of the wet friction clutch and the revolution of the engine; gradually disconnecting the wet friction clutch from a connected state by altering the duty ratio; and, when the difference between the revolution of the input side of the wet friction clutch and the engine revolution becomes less than a prescribed revolution during the foregoing process, learning the duty ratio at such time as the torque point upon making the electronic control unit initially learn the torque point for transmitting a prescribed torque when the wet friction clutch is connected from a disconnected state.
Here, it is preferable that the starting condition of the aforementioned torque point learning includes the conditions of a stopped vehicle, parking brake in use, foot brake in use, and transmission in use. The present invention is also a clutch control method for controlling the disconnection/connection of a clutch by altering the working fluid pressure for driving the disconnection/connection of a wet friction clutch in accordance with the duty pulse output from the electronic control unit, comprising the steps of:
outputting, from the electronic control unit, a prescribed start duty such that the clutch is initially connected broadly up to a point close to the torque point, when connecting the clutch from a disconnected state;
then outputting, from the electronic control unit in prescribed time intervals, such a prescribed gradual connection duty as to gradually connect the clutch;
retaining the start duty after the start duty is output; and
commencing the output of the aforementioned gradual connection duty after a predetermined time longer than the aforementioned prescribed time elapses.
Further, the present invention is also A method of learning a torque point of a clutch in a power transmission device of a vehicle in which a fluid coupling and a wet friction clutch are provided in series in the middle of a power transmission path extending from the engine up to the transmission, so that the disconnection/connection state of the clutch is controlled by changing the working fluid pressure for controlling the disconnection/connection of the clutch in accordance with the duty ratio of the duty pulse output from an electronic control unit, comprising the steps of:
when the aforementioned electronic control unit is caused to learn a torque point at which a prescribed torque is transmitted initially while the wet friction clutch is being connected from the disconnected state thereof, detecting the revolution of the input side of the clutch and the revolution of the engine, respectively;
initially outputting, from the electronic control unit, a start duty such that the clutch is connected broadly up to a point close the torque point;
then outputting, from the electronic control unit, a prescribed gradual connection duty in prescribed time intervals such that the clutch is connected gradually;
retaining the start duty after the aforementioned start duty is output, and commencing the output of the aforementioned gradual connection duty after a predetermined time longer than the aforementioned prescribed time elapses; and
when the revolution of the input side of the clutch becomes less than the engine revolution by a prescribed value of revolution during the foregoing process, learning the duty ratio at this time as the torque point.
Here, it is preferable that the learning is conducted after a predetermined time that is longer than the aforementioned prescribed time elapses from the time the decrease in the aforementioned prescribed revolution is detected.
The present invention is also a clutch control method for controlling the disconnection/connection of a clutch by altering the working fluid pressure for driving the disconnection/connection of a wet friction clutch in accordance with the duty pulse output from the electronic control unit,
wherein, when the clutch is connected from the disconnected state thereof, a start duty is first output from the electronic control unit, the aforementioned start duty being predetermined such that the clutch is connected broadly up to a point close to the torque point and the generation of excess clutch connection shock is constantly avoided in consideration of variances of the torque point;
a first gradual connection duty is then output from the electronic control unit in prescribed time intervals so as to gradually connect the clutch; and
a second gradual duty is output from the electronic control unit in prescribed time intervals such that the clutch is gradually connected slowly from the time a prescribed condition is satisfied.
Here, it is preferable that the wet friction clutch is provided in series with a fluid coupling in the middle of a power transmission path extending from the engine up to the transmission in a vehicle, and the aforementioned prescribed condition is established when the difference between the engine revolution and the clutch input side revolution exceeds a prescribed value.